<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .main {
            width: calc(100% - 36px);
            /* height: 500px;    //一定不要设置高度 */
            margin: 16px;
            background-color: pink;
            border-radius: 15px;
            aspect-ratio: 16/8;
        }
    </style>
</head>

<body>
    <div class="main"></div>
</body>

</html>